ACTUAL difference of Incremental and Differential Bkups ?

Discussion in 'Acronis True Image Product Line' started by Sunshine803, Mar 21, 2007.

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  1. Sunshine803

    Sunshine803 Registered Member

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    Hi everybody!...
    I am new to the forum which I think is a great source of info for all ATI users. I cannot stop thinking how little I know when I read the comments some of you experts here post. I have been using ATI for a few months, mainly to do total image bkups. I am confused with how ATI works regarding Incr and Diff Bkups.

    I think I understand the idea behind both. In Incremental you get the baseline plus several incremental ones (2,3,4 etc). Therefore, if you wanted to get back to the stage you were when you created say no.3, you select no. 3 and your data is restored as at that date. This is why all the incrementals are kept.

    In Differential, you get the baseline and one extra, no 2 which represents the changes against the baseline. It says in the manual that with the Diff you cannot recover to any intermediate stage, you HAVE to recover to the latest (or of course to the Baseline).

    My questions are:
    1. Why does ATI create Differentials with numbers greater than 2 and also keeps the previous ones?

    2. If during a Differential restore I select say no. 3, will I restore to the stage that I created no.3? If so, what is the difference to the Incrementak bkup?

    3. In the Help Manual somewhere it states that Differential bkups take up more space than the Incrementals . Shouldn't that be the opposite (if my understanding of the two definitions is right)?

    I look forward to your comments. BTW, I think that ATI is a super utility that no PC should be without it. It affords you peace of mind against anything that may threaten tour system and data. Well done to the Acronis Team.
     
  2. Tabvla

    Tabvla Registered Member

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    Hi Sunshine803, Welcome to the Forum....:D

    I could answer your question(s) but that may not be as helpful as you may think.

    You will learn considerably more if you do the following:

    - On a spare disk or partition create a Folder and call it ATI_Tests

    - From your My Documents Folder select a few Files and Folders about 250MB

    - Copy these files to a Folder ATI_Tests\Source

    - Now, using these files and the test folder, experiment with all the ideas that you have.... Backup, Restore, Incremental, Differential, Backup Locations, Scheduled Backups..... and so on.

    You will be amazed at how much you will learn.

    Come back and ask questions when you get stuck.

    :)
     
  3. Sunshine803

    Sunshine803 Registered Member

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    Sorry to persist with this but after my post above I carried out an experiment backing up and modifying 3 files and then doing a series of:
    1. Differential Bkups
    2. Incremental Bkups.

    To my surprise the 2 sets were identical. I could restore back to the baseline from both sets (as expected) and I could recover to ANY stage from 1st to last using both sets (not as expected...)

    So my 'desperate cry' to anybody that can answer (PLEASE!...)
    "What is the REAL difference between the two backup types" o_O?
    (My test results are identical)

    Thank you :'(
     
  4. Sunshine803

    Sunshine803 Registered Member

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    Hi Tabvla...
    Thanks for your reply. Unfortunately it came a few seconds after my 2nd post.
    You are absolutely right that one can learn a lot by playing around. I did, and I also learned a lot from reading up on several items I came across while practising with ATI.

    Still, my question still stands: ATI 'behaves' in identical manner for both types of bkups (incremental & differential). While I understand the difference between the two, I cannot for the life of me see ANY difference in the Acronis results. If in the Differential bkups it keeps the previous files all the way back to the original (baseline) then what is the difference between the two? And why in the Help manual does it say that Differential bkup needs more space).

    Could you PLEASE, if not much trouble, list the things you can and cannot do with each type of these two bkups (or at least the REAL difference between them)?

    Thanks and best regards
     
  5. Tabvla

    Tabvla Registered Member

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    No problem.... let me try again
    IMPORTANT :

    This example ignores the normal file compression that will occur when you backup. The numbers are for illustration only, just to get the idea across.

    Let us assume that we start with a folder called MyFiles that contains 50 files with filenames of "File_01" going up to "File_50" and a total size of 200MB.

    1. The first FULL backup results in a MyBackup_1.tib file of 200MB consisting of 50 files.

    2. Now we add another 10 files to the MyFiles folder named "File_51" to "File_60" with a size of 50MB.

    3. Create an Incremental backup. This will result in a new file MyBackup_2.tib of 50MB containing the 10 new files

    OR

    3. Creae a Differential backup. This will result in a new file MyBackup_2.tib of 50MB containing the 10 new files

    At this point there is NO difference between the processes.

    4. Now we add another 20 files to the MyFiles folder named "File_61" to "File_80" with a size of 100MB

    5. Create an Incremental backup. This will result in a new file MyBackup_3.tib of 100MB containing the 20 new files

    OR

    5. Create a Differential backup. This will result in a new file MyBackup_3.tib of 150MB containing the 30 new files.

    NOW there IS a difference.

    6. Now we add another 30 files to the MyFiles folder named "File_81" to "File_110" with a size of 150MB

    7. Create an Incremental backup. This will result in a new file MyBackup_4.tib of 150MB containing the 30 new files

    OR

    7. Create a Differential backup. This will result in a new file MyBackup_4.tib of 300MB containing the 60 new files.

    Now we have a BIG difference.

    Does that make sense? If not go and actually try it out. But don't do it with 2 or 3 little files. Do it with a substantial number of files that together are a substantial size. ATI backs-up data files very quickly so it won't take all that much time.
     
  6. Sunshine803

    Sunshine803 Registered Member

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    Thank you VERY much TABVLA

    I really appreciate the fact that you took the trouble to explain so well in such clear detail.

    Now I know how ATI 'behaves'. I find it a little odd that the intermediate .tib's are kept in Differentials.
    I suppose, to allow the user to revert back to any of the stages if needed,
    contrary to what I read in some manual.

    I tabulated the figures in your example (for visual clarity) showing both
    the number of files and disk space taken up:

    Stage-----SOURCE------INCRL----------DIFFL------File

    A----------50/200------50/200--------50/200-----1.tib
    B-------+--10/ 50------10/ 50---------10/ 50-----2.tib
    C-------+--20/100------20/100--------30/150-----3.tib
    D-------+--30/150------30/150--------60/300-----4.tib

    Totals:----110/500-----110/500-------150/700

    It appears that the only advantage of Differential is a faster restore but it
    must also be a slower backup and more disk space. I assume that the user
    can delete the intermediate files unless he/she wants to have the comfort
    of reverting to any stage other than the last.

    Personally I'd choose the Incremental. I'd rather have quicker backups and
    less space taken up than worry about the extra time it takes to restore (if ever needed)

    Again Tabvla, thank you VERY much for helping to clarify a significant point
    which is not very well explained in the manuals.

    :thumb: Cheers :)
     
  7. aggronix

    aggronix Registered Member

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    But note:

    Assume that you make (for example) one full Backup on Sunday and then incremental backups on Monday, Tuesday, ..,Friday.

    If you have a headcrash on Saturday you'll need your full backup (Sunday) and every day's incremental backup to restore what you had on friday evening. If one of your incremental backup is lost you can only restore to a point in time before.

    If you made differential backups, you'll need only your sunday's full backup and only one differential backup - the one of friday.

    Therefore you can overwrite a monday's differential backup if your thursday's is valid. (or- for more safety - overwrite a monday's differential backup if your thursday's and wednesday's are valid).

    see also here: http://en.wikipedia.org/wiki/Incremental_backup
    regards, aggronix.
     
  8. Tabvla

    Tabvla Registered Member

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    Glad to be of help.

    The post by "aggronix" is very important, so please note carefully.

    Finally there is one potential issue....
    I recall that in ATI v9.x there was a bug which required ALL Differentials to be present in order to perform an archive validation. I have not personally tested whether this issue has been fixed in ATI v10. Perhaps someone would test and report back to the Forum...:)

    T.
     
  9. Sunshine803

    Sunshine803 Registered Member

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    Thanks Aggronix, useful info to bear in mind.
    There is no perfect method it seems, there are always pros and cons...
    Plus an element of risk whatever you do.
    But then again, what would life be like without the excitement of overcoming some risks!...

    Best regards :)
     
  10. brettr

    brettr Registered Member

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    One important reason to use incrementals is for more granular restoring. Using one of the above examples, say I do a full backup every Sunday and incrementals on all other days. I write software and backup my source code this way. If something happens on Wednesday and I want to see the entire state of affairs from Monday, I can restore my entire setup to some location and get all of the details I need. It's an audit trail with the ability to put you at some previous point in time. If I'd done a differential on Tuesday, I couldn't take a look at the entire setup as it existed on Monday.

    Regards,
    Brett
     
  11. robmeyer

    robmeyer Registered Member

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    Reading all this, I realize that I keep all differentials in the backuplocation for as long as I want. If the number of differentials is getting too long, I delete some of earlier date.
    Be aware that TI starts numbering the differentials from the first missing number. So if your full backup was numbered 1 to 4 and there were 30 differentials while you deleted 5 to 25, TI numbers the next baxkup as 5 !!

    Rob
     
  12. Tabvla

    Tabvla Registered Member

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    Hi Rob, welcome to the Forum... :D

    Please be aware that there has been a bug in ATI since the early days, which still persists in ATI v10.

    The bug requires that ALL differentials in an archive be present to enable the archive to be validated. Therefore if you delete any differential in a series you will not be able to validate the latest differential because ATI will "look" for all previous differentials, since the creation of the first full backup, and return an error when it cannot find a deleted differential.

    This Forum has for a very long time been asking Acronis to fix this bug.... but to date Acronis have decided to simply ignore what is a fundamental flaw in the product that limits the usability of the differential backup process.

    Annoying..... really annoying :thumbd:

    T.
     
  13. Acronis Support

    Acronis Support Acronis Support Staff

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    Hello Sunshine803,

    Thank you for choosing Acronis Disk Backup Software.

    Please see chapter 3.2 "Full, incremental and differential backups" of the respective User's Guide for detailed information on types of backups.

    Thank you.
    --
    Marat Setdikov
     
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